Aerobic biological processes are commonly used in the treatment of industrial wastewater, before discharge to the environment. In such processes micro-organisms consume wastewater contaminants, and are encouraged to proliferate in reactor systems under intensive aeration. A variety of process configurations are known, such as activated sludge, moving bed biofilm reactors, membrane bioreactors, aerated lagoons and aerated stabilisation basins. Aerated lagoons and aeration stabilisation basins are examples of low rate biological treatment systems, whilst activated sludge and variant systems and moving bed biofilm reactors are high rate biological treatment systems.
Pulp and paper mill wastewaters are typically deficient in nutrient nitrogen required to support bacterial growth for biological treatment. Conventionally activated sludge processes used in the pulp and paper industry are operated with the addition of nitrogen to the system, typically in the form of urea. Other industrial wastewaters can also be nitrogen-deficient. By “nitrogen-deficient wastewater” is meant wastewater for which, due to lack of available nitrogen in the wastewater, an additional nitrogen source is required for the biological consumption of the biodegradable organic material present.
It has also previously been proposed to use industrial wastewaters to produce biopolymers having economic value. For example Japanese patent application 3143397 discloses a method for the production of a polyhydroxyalkanoate (PHA) wherein a carbon source is added to an activated sludge so as to raise microbial numbers. Denitrification of this culture is then required prior to its aerobic culture under nitrogen deficient conditions to achieve the intracellular accumulation of polyhydroxybutyric acid. Japanese patent 2514131 requires wastewater to be treated to undergo an initial anaerobic acid fermentation so as to achieve a conversion of the organic content of the wastewater to carboxylic acids. The fermented wastewater then undergoes a nitrogen removal step prior to its use as a feed for nitrogen fixing micro-organisms. Application of this method for the production of polymers, such as PHAs accumulated in the nitrogen-fixing micro-organisms, is also disclosed. Both methods require removal of nitrogen in a separate step, prior to the use of the wastewater for the production of polymer.